Costs for the heating & sanitary trade

Yes, it remains an option that I can possibly take. But it also doesn't help me if he then insists on the contract and then his old (or a new one, it doesn't matter) subcontractor strictly executes according to the construction service description with a non-eligible heat pump and without controlled residential ventilation.
So, I currently see the chances of enforcing my claims rather in external contracting.
I already have quite a lot that I assign myself with windows, stairs, and probably interior doors and earthworks. One more doesn't make a difference.
Basically, I will soon have a shell construction plastered inside and outside with electrical work, architect planning, and construction management delivered for just under 200,000 EUR... Is that still okay?

Sanitary installations are quite different from interior doors, etc....

The sanitary installer needs breakthroughs/slits/recesses, needs power at the right places, where does the distribution for underfloor heating go, and so on.

I personally supervised individual contracting.
But in no trade was I so glad that the companies knew each other and I didn’t have to play the middleman...
In the shell construction, the sanitary installer asked me where the distribution should go. I decided, and he coordinated the entire execution (size of the opening, dimensions of the lintel, etc.) directly with the mason.

How is it supposed to work with you?

The sanitary installer tells you,
"I need power at the heat pump."
You go to the general contractor
"Sanitary needs power."
General contractor to the electrician
"Client needs power at the heat pump."
Electrician:
"3-core or 5-core? Control cable? ..."

Then the whole chain goes up and down again, and in the end it’s different anyway.... And who is to blame then?

And as you say:
Who does the insulation?

And who does the screed in between?

What thickness?

What thickness is the underfloor heating pipe from the plumber, that is immensely important for the coverage.

Does the plumber use prefabricated panels (=less insulation) or does he staple directly onto the insulation?

Oh, I see, yes, I understand that. Everything is already planned. So I would basically tender with the planning. The new heating/plumbing guy should then carry out the work as previously intended (just including my quantity takeoffs and with the installation plan from the MEP office). Of course, if he acts like the old one (I know everything better), it won’t work, but I’m hoping to find someone who, if he isn’t tied to a general contractor and knows from the start what’s going on—not just getting all the info piecemeal afterwards through quantity takeoffs and claims—will set the right price for himself accordingly and execute without complaints. The site manager will still coordinate everything, including the external trades. Sure, I have to be careful and establish contact, and I won’t blindly rely on everything running smoothly by itself. But it’s not like I’m starting from scratch and have to manage everything alone.

And as you say: Who does the insulation? And who does the screed in between? What thickness? What thickness is the pipe of the underfloor heating from the plumber, that is immensely important for the coverage. Does the plumber use prefabricated panels (=less insulation) or does he staple directly onto the insulation?

The execution planning for this is available. I myself just don’t know who usually owes what. If it’s usually done by the heating installer, that’s fine. I just wanted to know if I can quasi deduct something from my calculated costs to get closer to the costs of the general contractor. So for example: "Ok, you don’t want to credit me anymore, but then you do the insulation." But I hear that this would be a bad idea.

Are you off during the construction phase, or can you check on things at any time, or only on weekends? That would be an important criterion for me to (not) make you the site manager for the own trades.